1. Field of the Invention
This invention relates to a method for making a rigid cellular structure by coating and firing a composition comprising aluminum powder and organic titanate ester on a porous, sacrificial substrate. The structure prepared by the method of this invention are useful as catalytic supports which can be electrically heated, or as flow-through type electrical heating elements which afford rapid heat transfer to liquids and gases flowing therethrough.
2. Description of the Prior Art
U.S. Pat. No. 3,111,396 discloses a method for making a low density, porous, inherently electrically conductive metal or metal compound foam, which method comprises (a) impregnating a porous organic structure with powdered material in a fluid, (b) slowly drying the impregnated organic structure, (c) heating the impregnated organic structure slowly to decompose the organic structure and fluid to a weakly bonded carbon structure while closely retaining the shape and size of the original organic structure, and (d) sintering the impregnated carbon-powdered material at high temperature to further join the powder in a continuous form.
A typical impregnating slurry of U.S. Pat. No. 3,111,396 is made of a liquid such as an organic solvent or water, a metal, metal oxide, or other metal compound in powder form, and usually a decomposable binder. In one embodiment, a powdered nickel base alloy is oxidized to form an oxide of the alloy which is then slurried with binder and water. Active heating steps of the method, when carried out in a reducing atmosphere of hydrogen, result in a brittle or ductile foam of the original unoxidized alloy depending on the chemical reactivity of the binder used.
In contrast to the teaching of U.S. Pat. No. 3,111,396, the present invention provides a rapid method for producing an electrically conductive, rigid cellular structure having high compressive strengths of, preferably, at least 50 psi, without the need for slow carbonization to achieve bond strength of an intermediate structure during processing, without the need for prolonged sintering at high temperatures, and without the need for oxidation and subsequent reduction in an atmosphere of hydrogen. Concerning the successively higher heating steps taught in U.S. Pat. No. 3,111,396, the reference teaching is summarized in column 2, at lines 27 to 43. Further, the organic substrate structures of the instant invention are removable and are removed in the process disclosed herein. The process of U.S. Pat. No. 3,111,396, on the other hand, teaches the slow carbonization of the substrate to leave a cohesive residue as a support for the metallic component.